The present invention relates to wireless communication and, more particularly, to a method and apparatus in which user equipment transmits aperiodic channel state information in a wireless communication system.
The data transfer rate over a wireless communication network is recently rapidly increasing. This is because a variety of devices, such as smart phones and tablet PCs which require Machine-to-Machine (M2M) communication and a high data transfer rate, are appearing and spread. In order to meet a higher data transfer rate, carrier aggregation technology and cognitive radio technology for efficiently using more frequency bands and multiple antenna technology and multiple base station cooperation technology for increasing the data capacity within a limited frequency are recently are highlighted.
Furthermore, a wireless communication network is evolving toward a tendency that the density of accessible nodes around a user is increasing. Here, the term ‘node’ may mean antennas or a group of antennas which are spaced apart from one another in a Distributed Antenna System (DAS). However, the node is not limited to the meaning, but may be used as a broader meaning. That is, the node may become a pico eNB (PeNB), a home eNB (HeNB), a Remote Radio Head (RRH), a Remote Radio Unit (RRU), or a relay. A wireless communication system including nodes having a high density may have higher system performance through cooperation between nodes. That is, if the transmission and reception of each node are managed by one control station so that the nodes are operated as antennas or a group of antennas for one cell, the node may have much more excellent system performance as compared with when the nodes do not cooperate with each other and thus each node operated as an independent Base Station (BS) (or an Advanced BS (ABS), a Node-B (NB), an eNode-B (eNB), or an Access Point (AP)). A wireless communication system including a plurality of nodes is hereinafter referred to as a multi-node system.
In a multi-node system, a node which sends a signal to user equipment may be different every user equipment, and a plurality of the nodes may be configured. Here, the nodes may send different reference signals. The reference signals transmitted by the respective nodes may be transmitted in different subframes because the reference signals have different subframe offset values although they have the same transmission cycle. In this case, it may be necessary for a base station to request user equipment to measure a plurality of reference signals transmitted in different subframes and feedback the measurement. In the prior art, a channel state information request field is transmitted in each downlink subframe in which a reference signal, that is, the subject of measurement is transmitted. The conventional method is problematic in that radio resources are wasted because a channel state information request field must be repeatedly transmitted.